1. Field of the Invention
The invention relates to an LED lamp, and more particularly to a light-emitting device including a blue LED chip and a wavelength conversion material in combination. The light-emitting device is configured such that light emitted from the LED chip excites the fluorescent material. The light from the LED chip is mixed with light from the fluorescent material to obtain white light or a middle color light.
2. Description of Related Art
FIG. 5 shows a conventional art structure employed to obtain a pseudo-white LED lamp 90 with a blue LED chip 91 and a yellow fluorescent material 92 in combination. An element substrate 93 formed of a printed circuit board has two-polarity circuits 93a with positive and negative polarities formed thereon by appropriate means, such as etching. The LED chip 91 is die-bonded to the one polarity.
The LED chip 91 is wired through a gold wire 94 to the other polarity to supply power to the LED chip 91. The LED chip 91 is molded in a transparent sealing resin 95 such as epoxy to form a case 96 to protect both the LED chip 91 from humidity and the gold wire 94 from breaking due to mechanical stresses.
For formation of the white LED lamp 90 in particular, an appropriate amount of the fluorescent material 92 is mixed in the transparent resin 95 because the light emitted from the LED chip 91 is blue. In this case, the fluorescent material 92 causes yellow fluorescence when excited by the light emitted from the LED chip 91. As a result, the light discharged externally from the case 96 can be seen as white light after mixture of blue and yellow light which have a complementary relation therebetween (see U.S. Pat. No. 6,482,664, which is hereby incorporated in its entirety by reference).
In the white LED lamp 90 having the above-described conventional art structure, as shown in FIG. 5, different directions from which the LED lamp 90 is viewed results in differences in distance over which the light emitted from the LED chip 91 travels within the case 96 to the viewer. Therefore, depending on the viewing direction, blue light may collide with the fluorescent material 92 a different number of times.
As a result, the light seen at an angle, which makes a longer transmission distance in the sealing resin 95, is strongly tinged with yellow, and the light seen at an angle in which a shorter distance is traveled, is strongly tinged with blue. Thus, the color may feel as if it changes depending on the viewing direction, and variations in color may be felt depending on the shapes even when viewed in a single direction.